Application issues for large-area electrochromic windows in commercial buildings

Projections of performance from small-area devices to large-area windows and enterprise marketing have created high expectations for electrochromic glazings. As a result, this paper seeks to precipitate an objective dialog between material scientists and building-application scientists to determine whether actual large-area electrochromic devices will result in significant performance benefits and what material improvements are needed, if any, to make electrochromics more practical for commercial building applications.Few in situ tests have been conducted with large-area electrochromic windows applied in buildings. This study presents monitored results from a full-scale field test of large-area electrochromic windows to illustrate how this technology will perform in commercial buildings. The visible transmittance (T_v) of the installed electrochromic ranged from 0.11 to 0.38. The data are limited to the winter period for a south-east-facing window. The effect of actual device performance on lighting energy use, direct sun control, discomfort glare, and interior illumination is discussed. No mechanical system loads were monitored. These data demonstrate the use of electrochromics in a moderate climate and focus on the most restrictive visual task: computer use in offices.Through this small demonstration, we were able to determine that electrochromic windows can indeed provide unmitigated transparent views and a level of dynamic illumination control never before seen in architectural glazing materials. Daily lighting energy use was 6–24% less compared to the 11%-glazing, with improved interior brightness levels. Daily lighting energy use was 3% less to 13% more compared to the 38%-glazing, with improved window brightness control. The electrochromic window may not be able to fulfill both energy-efficiency and visual comfort objectives when low winter direct sun is present, particularly for computer tasks using cathode-ray tube (CRT) displays. However, window and architectural design as well as electrochromic control options are suggested as methods to broaden the applicability of electrochromics for commercial buildings. Without further modification, its applicability is expected to be limited during cold winter periods due to its slow switching speed.     

Lighting and energy performance of solar film coating in air-conditioned cellular offices

In subtropical Hong Kong, the principal objectives of fenestration design include eliminating direct sunlight and decreasing cooling loads. To avoid the problems of glare, excessive brightness and thermal discomfort, occupants may block the windows with internal shading devices, resulting in poor daylighting performance and very small amount of electric lighting energy savings. Recently, the advances in thin film coatings for window glass products provide a means of substantially reducing heat gain without proportionally reducing daylight transmittance. It has been suggested that film coatings together with photoelectric lighting control systems could minimise the electric lighting and cooling requirements without causing undue visual and thermal discomfort to the occupants. This paper presents field measurements on solar control film coatings in fully air-conditioned offices in Hong Kong. Solar heat gains, indoor illuminance levels and the electricity consumption by the fluorescent luminaires were systematically recorded and analysed. Measurements were made for two cellular offices, one with solar control film coating on the window glass and the other without. The findings showed that the solar film coating could cut down energy expenditures for air-conditioned buildings, especially for spaces with large glazing areas subject to substantial amount of direct sunlight. Results are presented and the design implications discussed.     

Daylighting performance evaluation of a bottom-up motorized roller shade

This paper presents an experimental and simulation study for quantifying the daylighting performance of bottom-up roller shades installed in office spaces. The bottom-up shade is a motorized roller shade that opens from top to bottom operating in the opposite direction of a conventional roller shade, so as to cover the bottom part of the window, while allowing daylight to enter from the top part of the window, reaching deeper into the room. A daylighting simulation model, validated with full-scale experiments, was developed in order to establish correlations between the shade position, outdoor illuminance and work plane illuminance for different outdoor conditions. Then, a shading control algorithm was developed for application in any location and orientation. The validated model was employed for a sensitivity analysis of the impact of shade optical properties and control on the potential energy savings due to the use of daylighting. The results showed that Daylight Autonomy for the bottom-up shade is 8–58% higher compared to a conventional roller shade, with a difference of 46% further away from the façade, where the use of electric lighting is needed most of the time. The potential reduction in energy consumption for lighting is 21–41%.     

The impact of shading design and control on building cooling and lighting demand

Shading should be considered as an integral part of fenestration system design for commercial and office buildings, in order to balance daylighting requirements versus the need to reduce solar gains. In this paper, the simultaneous impact of glazing area, shading device properties and shading control on building cooling and lighting demand was calculated using a coupled lighting and thermal simulation module. The interactions between cooling and lighting energy use in perimeter spaces were evaluated as a function of window-to-wall ratio and shading parameters. An exterior roller shade was used as an example. The impact of shading device type, properties and control on building cooling and lighting energy demand was quantified and analyzed. The simulation results indicate that, if an integrated approach for automatic control of motorized shading is used in conjunction with controllable electric lighting systems, substantial reduction of energy demand for cooling and lighting could be achieved in perimeter spaces, depending on climatic conditions and orientation.     

An analysis of light-pipe system via full-scale measurements

Daylighting is an effective sustainable development strategy to alleviating the problems in energy and the environment, and improving the qualities for visual comfort and health. In Hong Kong, many buildings are high-rise blocks constructed close to each other resulting in severe sky obstructions. Recently, a great deal of attention has been paid to the development of natural daylight exploitation products. One invention is the light-pipe system that transports natural light efficiently from outdoor into rear part of a room. However, this innovative daylighting device is not popular in subtropical Hong Kong. The main reason for such unenthusiastic responses is the lack of local data to indicate the visual performance, energy savings and design implications. A research project was initiated to evaluate these issues. The study includes field measurements of daylight illuminance in a corridor installed a number of light pipes. The results demonstrate that the light-pipe system can provide sufficient illuminance, improve the daylight uniformity and have a high potential to reduce the electric lighting energy consumption.     

遮阳板在建筑节能中的应用研究

太阳辐射对供暖、空调负荷有重要的影响。在中国北方地区的建筑物的窗和墙面上，夏天希望尽可能的减少太阳照射，而冬天则希望多得到太阳照射。因此，遮阳板的合理设计就成为建筑节能的一个重要途径。该文根据天津地区典型气象年的气象资料，对该地区建筑南向窗遮阳板的构造进行建模分析，并对其节能前景进行预测。考虑到建筑物美观、遮阳板自身材料及建筑的层高等因素，在保证冬季的日照的前提下，天津地区南向窗遮阳板宽度宜取0．5～0．9m，距窗户上沿距离0．5～0．8m。安装遮阳板后，南向窗每个夏季可减少太阳辐射得热80～110MJ/m^2。     

DAYLIGHTING TECHNOLOGIES IN NON-DOMESTIC BUILDINGS

Natural daylight is an inexpensive and very efficient light source provided that the amount of daylight entering a building is controlled according to demand. In commercial buildings electricity for lighting can be cut by 50-75% using daylighting design techniques in combination with efficient artificial lighting. New lighting control technologies and advanced computer simulation tools lo optimize large buildings makes it possible to exploit these energy savings.

Daylight is a very efficient light source, providing more light for less input of thermal energy than any other artificial light source. Efficient shading systems are now emerging systems that can control the admission of daylight to the room according to requirement, and avoid overheating. Some of these systems, such as reflective light shelves, will also contribute to a better distribution of the daylight available by redistributing some daylight to the back of the room. However, more work is needed to develop and test such combined daylight and shading systems.

The use of daylight to reduce electric lighting must be seen as an integrated part of the overall energy optimization of the building. An efficient control of the use of daylight and artificial lighting will not only reduce electricity use for lighting. Additionally, the use of electricity for ventilation and cooling can be reduced also, because the internal heat gains provocating these electricity uses are reduced. This calls for an integrated design approach to the overall energy design of the building, involving the architect and the engineer from the very beginning of the design phase.

Visual comfort of office buildings receives increasing attention, partially because of the VDU's (Visual Display Units) of the computers, that are now almost standard equipment of every work place. The performance requirements for both daylighting systems and artificial lighting systems have been sharpened, and the attention to this fact is crucial in future development of lighting systems.     

办公建筑遮阳产品综合性能模拟与评价

该文旨在探究卷帘对夏热冬冷地区办公建筑采光和能耗的综合影响并确定影响卷帘综合性能的关键参数。首先，选取影响卷帘性能的6个参数：太阳辐射透过率、太阳辐射反射率、红外透射率、外侧发射率、内侧发射率和导热系数；组合得到560种遮阳产品，并利用EnergyPlus软件和Radiance软件对其进行全年动态能耗模拟和全年采光模拟；其次，通过调查问卷获得考虑办公建筑人员行为的遮阳时间表以及室内人员对眩光、自然采光和能耗的关注度占比；最后，综合考虑能耗、眩光和自然采光，创新性地提出综合性能指标（ED）对卷帘进行综合评价。基于该指标，确定影响卷帘性能的关键参数。研究结果表明，在夏热冬冷地区，太阳辐射透过率和太阳辐射反射率是影响卷帘综合性能的关键参数，当太阳辐射透过率在0.01～0.10范围内变化时，其对卷帘综合性能有积极影响。     

Quantifying the potential of automated dynamic solar shading in office buildings through integrated simulations of energy and daylight

The façade design is and should be considered a central issue in the design of energy-efficient buildings. That is why dynamic façade components are increasingly used to adapt to both internal and external impacts, and to cope with a reduction in energy consumption and an increase in occupant comfort. To gain a complete picture of any façade’s performance and subsequently carry out a reasonable benchmarking of various façade alternatives, the total energy consumption and indoor environment need to be considered simultaneously. We quantified the potential of dynamic solar shading façade components by using integrated simulations that took energy demand, the indoor air quality, the amount of daylight available, and visual comfort into consideration. Three types of façades were investigated (without solar shading, with fixed solar shading, and with dynamic solar shading), and we simulated them with various window heights and orientations. Their performance was evaluated on the basis of the building’s total energy demand, its energy demand for heating, cooling and lighting, and also its daylight factors. Simulation results comparing the three façade alternatives show potential for significant energy reduction, but greater differences and conflicting tendencies were revealed when the energy needed for heating, cooling and artificial lighting were considered separately. Moreover, the use of dynamic solar shading dramatically improved the amount of daylight available compared to fixed solar shading, which emphasises the need for dynamic and integrated simulations early in the design process to facilitate informed design decisions about the façade.     

Modelling Complex Fenestration Systems using physical and virtual models

Physical or virtual models are commonly used to visualize the conceptual ideas of architects, lighting designers and researchers; they are also employed to assess the daylighting performance of buildings, particularly in cases where Complex Fenestration Systems (CFS) are considered. Recent studies have however revealed a general tendency of physical models to over-estimate this performance, compared to those of real buildings; these discrepancies can be attributed to several reasons. In order to identify the main error sources, a series of comparisons in-between a real building (a single office room within a test module) and the corresponding physical and virtual models was undertaken. The physical model was placed in outdoor conditions, which were strictly identical to those of the real building, as well as underneath a scanning sky simulator. The virtual model simulations were carried out by way of the Radiance program using the GenSky function; an alternative evaluation method, named Partial Daylight Factor method (PDF method), was also employed with the physical model together with sky luminance distributions acquired by a digital sky scanner during the monitoring of the real building. The overall daylighting performance of physical and virtual models were assessed and compared. The causes of discrepancies between the daylighting performance of the real building and the models were analysed. The main identified sources of errors are the reproduction of building details, the CFS modelling and the mocking-up of the geometrical and photometrical properties. To study the impact of these errors on daylighting performance assessment, computer simulation models created using the Radiance program were also used to carry out a sensitivity analysis of modelling errors.The study of the models showed that large discrepancies can occur in daylighting performance assessment. In case of improper mocking-up of the glazing for instance, relative divergences of 25-40% can be found in different room locations, suggesting that more light is entering than actually monitored in the real building. All these discrepancies can however be reduced by making an effort to carefully mock up the geometry and photometry of the real building. A synthesis is presented in this article which can be used as guidelines for daylighting designers to avoid or estimate errors during CFS daylighting performance assessment.     

Lighting and cooling energy consumption in an open-plan office using solar film coating

In subtropical Hong Kong, solar heat gain via glazing contributes to a significant proportion of the building envelope cooling load. The principal fenestration design includes eliminating direct sunlight and reducing cooling requirements. Daylighting is an effective approach to allow a flexible building façade design strategy, and to enhance an energy-efficient and green building development. This paper studies the lighting and cooling energy performances for a fully air-conditioned open-plan office when solar control films together with daylight-linked lighting controls are being used. Measurements were undertaken at two stages including the electricity expenditures for the office using photoelectric dimming controls only (first stage) and together with the solar control film coatings on the windows (second stage). Electric lighting and cooling energy consumption, transmitted daylight illuminance and solar radiation were systematically recorded and analysed. The measured data were also used for conducting and validating the building energy simulations. The findings showed that the solar film coatings coupled with lighting dimming controls cut down 21.2% electric lighting and 6.9% cooling energy consumption for the open-plan office.     

Determining photosensor settings for optimum energy saving of suspended lighting systems in a small double‐skinned office

A photoelectric dimming control system applied to a suspended direct/indirect and indirect lighting system was analyzed to determine effective control options in a small office with double‐skin envelope. Computer simulations were performed for photosensors positioned at three different locations with three specific configurations under three Commission Internationale de l'Élairage standard sky types. Optimum ideal dimming level was determined for each combination of room orientation, photosensor configurations and positions. In general, fully shielded photosensors achieved better control performance among other configurations used for the photosensors on the ceiling and the back wall. The effect of photosensor configurations on dimming system performance was as significant as the photosensor positions. As the penetration of daylight decreased due to the shaded area on the internal envelope, the control system performance deteriorated. The correlation between the photosensor signals and the desktop illuminance levels due to daylight was not significantly meaningful under the lighting systems. Lighting energy savings were determined for the best and good system control performance. Copyright © 2009 John Wiley & Sons, Ltd.     

New component for daylighting: first italian application of a sun duct

The use of daylighting in a room is certainly better than the use of lamplight alone, due to its undubitable chromatic properties and correlated psychological effects. In many cases, especially for pre-existing buildings, the income of daylighting appears an unsolvable problem forcing people to use intensively electric lighting. In this paper the use of a component for natural lighting of a space with no direct openings to the exterior is presented. The project was carried out in a building situated in the old town centre of S. Colombano al Lambro near Milan.     

Computer-oriented building design: Advances in daylighting and thermal simulation tools

Advanced computer simulation tools for analyzing daylighting features and thermal performance of buildings are improved at the Fraunhofer Institute for Solar Energy Systems. For an analysis of daylighting elements in lighting simulations, new light-deflecting structures and materials have been measured and modeled. In order to study the interaction between lighting and thermal behaviour of rooms, thermal and lighting simulation techniques are linked together. Thus, integrated energy concepts can be evaluated. Programs for handling parallel image generation in a network of high-performance Unix workstations have been developed.     

Optimizing performance of the lightshelf by modifying ceiling geometry in highly luminous climates

The impact of ceiling geometries on the performance of lightshelves was investigated using physical model experiments and radiance simulations. Illuminance level and distribution uniformity were assessed for a working plane in a large space located in sub-tropical climate regions where innovative systems for daylighting and shading are required. It was found that the performance of the lightshelf can be improved by changing the ceiling geometry; the illuminance level increased in the rear of the room and decreased in the front near the window compared to rooms having conventional horizontal ceilings. Moreover, greater uniformity was achieved throughout the room as a result of reducing the difference in the illuminance level between the front and rear of the room. Radiance simulation results were found to be in good agreement with physical model data obtained under a clear sky and high solar radiation. The best ceiling shape was found to be one that is curved in the front and rear of the room.     

On-site performance of electrochromic glazings coupled to an anidolic daylighting system

This work takes benefit from two advanced building technologies through the integration of an anidolic daylighting system and an electro-chromic glazing in a building facade for achieving an optimal control of the daylight flux entering in an office room. Computer simulations of different systems configurations, based on ray-tracing techniques, were used to identify the optimal anidolic system design. Once installed in an experimental building the visual and thermal performance of the anidolic system coupled to an electrochromic glazing was assessed by way of on-site monitoring. These performances were compared to those offered by a conventional double glazing unit installed in an identical neighbouring room. An evaluation of users comfort was achieved by way of a survey involving 30 different subjects. Their visual performance during specific tasks performed on a VDT screen and/or on a sheet of paper was used to compare the lighting conditions. The main results of this detailed experimental study, showing the capability of such a combined daylighting system to control the daylight flux entering a working space, are presented in this paper.     

Light shade bands for the improvement of solar hydrogen production efficiency by Rhodobacter sphaeroides RV

At mid-day, the sunlight provides excessive energy for photo-hydrogen production by photosynthetic bacteria. Conversion efficiency from light energy to hydrogen decreased under high illumination. To overcome this problem, we examined a method to spatial dispersion of the high illumination. The new photobioreactor using the light shade bands set on the surface of the reactor was developed for efficient hydrogen production. Spatial dispersion gave remarkable effect on conversion efficiency under the excessive light condition. Indoors, the 1.0 cm width of light shade bands gave the best conversion efficiency (2.1%). Actual use of the sunlight, the 1.5 cm width of light shade bands provided the best conversion efficiency (1.4%). Light inhibition was successfully suppressed by the light shade bands in both experiments. The dispersed light energy could be used for other energy conversion device as solar cells.     

Using digital imaging to assess spectral solar-optical properties of complex fenestration materials: A new approach in video-goniophotometry

A large variety of angularly selective fenestration systems have been developed in the past two decades and show great potential in improving visual comfort while reducing energy consumption, especially when combined with spectrally selective properties. Such systems include light-redirecting glazing, shading, film coatings, reflectors and others. To assess the potential of these systems accurately and reliably, one needs to be able to predict in detail how they modify the energy, direction and spectral make-up of solar radiation. For this assessment, spectral (wavelength-dependent) Bidirectional Transmission or Reflection Distribution Functions are used, usually referred to as BTDFs or BRDFs, or more generally BSDFs for Scattering Functions.To enable a faster, cheaper, and continuous investigation of these properties over most of the solar spectrum (400-1700 nm), an innovative goniospectrometric instrument has been created, relying on digital imaging, on light collection by an ellipsoidal half-transparent mirror, and on a filtering method in the visible range to generate spectral radiometric BSDFs. This so-called Heliodome instrument is described in this paper. It enables the performance of new fenestration technologies to be assessed in terms of lighting and solar gains management potential. The rotating table also serves as a heliodon, an architectural design tool for visualizing sunlight distribution inside a scale model and performing analyses on appropriate sun control strategies. The Heliodome’s major innovations compared to other devices are to enable an analysis of both the visible and the near-infrared portions of the solar spectrum, to provide spectral as well as photometric light distribution data, and to ensure a continuous investigation of the transmitted or reflected light in a time-efficient way.     

An analysis of energy-efficient light fittings and lighting controls

Electric lighting is one of the major energy consuming items in many non-domestic buildings. Using appropriate energy-efficient light fittings with dimming controls and proper daylighting schemes can help reduce the electrical demand and contribute to visual comfort and green building development. This paper presents a study on the energy and lighting performances for energy-efficient fluorescent lamps associated with electronic ballasts and high frequency photoelectric dimming controls installed in a school building. Electricity expenditures and indoor illuminance levels for a workshop and a classroom employing high frequency dimming controls were analyzed. Simple prediction methods were used to illustrate the lighting savings. The findings provide the operational and performance information, which would be applicable to other spaces with similar building layouts and lighting schemes.     

A generalized window energy rating system for typical office buildings

Detailed computer simulation programs require lengthy inputs, and cannot directly provide an insight to relationship between the window energy performance and the key window design parameters. Hence, several window energy rating systems (WERS) for residential houses and small buildings have been developed in different countries. Many studies showed that utilization of daylight through elaborate design and operation of windows leads to significant energy savings in both cooling and lighting in office buildings. However, the current WERSs do not consider daylighting effect, while most of daylighting analyses do not take into account the influence of convective and infiltration heat gains. Therefore, a generalized WERS for typical office buildings has been presented, which takes all primary influence factors into account. The model includes embodied and operation energy uses and savings by a window to fully reflect interactions among the influence parameters. Reference locations selected for artificial lighting and glare control in the current common simulation practice may cause uncompromised conflicts, which could result in over- or under-estimated energy performance. Widely used computer programs, DOE2 and ADELINE, for hourly daylighting and cooling simulations have their own weaknesses, which may result in unrealistic or inaccurate results. An approach is also presented for taking the advantages of the both programs and avoiding their weaknesses. The model and approach have been applied to a typical office building of Hong Kong as an example to demonstrate how a WERS in a particular location can be established and how well the model can work. The energy effect of window properties, window-to-wall ratio (WWR), building orientation and lighting control strategies have been analyzed, and can be indicated by the localized WERS. An application example also demonstrates that the algebraic WERS derived from simulation results can be easily used for the optimal design of windows in buildings similar to the typical buildings.